AS/NZS 3008 Cable Installation & Derating

Overview

This page is a cross-cutting reference for the AS/NZS 3008.1.1 cable installation, current carrying capacity (CCC) rating, and derating factor system used across the four cable sizing calculators:

• c0006 — Motor Cable Sizing (3-phase)
• c0030 — Load Cable Sizing (3-phase)
• c0031 — Load Cable Sizing (1-phase)
• c0032 — Motor Cable Sizing (1-phase)

All four calculators share the same installation method options, CCC lookup mechanism, and derating factor computation. The CCC rating for a cable is looked up from StandardColumn records in the webcalcs database. Each CCC column stores a derating_table code that determines which grouping derating fields appear in the sidebar.

Installation Methods

Six installation methods are available, corresponding to clauses in AS/NZS 3008.1.1. The method determines which CCC tables apply and which environmental derating factors are relevant.

CCC Column Sub-Selection Fields

These sidebar fields refine the CCC column lookup within a given installation method. They are controlled by v-if on calculationForm.param_installation_method (and sometimes cable formation) because they must be set before the calculation runs — they determine which CCC column to look up.

Derating Table Codes

Each StandardColumn record stores a derating_table field. When the CCC is looked up, this code is returned in the API response as derating_table_code. It drives which grouping derating sidebar fields become visible.

Grouping Derating Fields

These sidebar fields appear based on the deratingTableCode value returned from the calculation API. Only one grouping table (22–26) applies per CCC column.

Environmental Derating Fields

Environmental derating fields remain controlled by installation_method v-if because they apply based on whether the cable is in air or buried — not based on the specific CCC column. Multiple environmental factors can apply simultaneously.

Derating Factor Computation

The combined derating factor is the product of all applicable individual factors. Only one grouping table (22–26) applies per CCC column, but multiple environmental tables can apply simultaneously.

Where:

• \( F_{group} \) — Grouping derating from one of Tables 22–26 (based on derating_table_code)
• \( F_{temp} \) — Temperature derating from Table 27.1 (air) or 27.2 (soil)
• \( F_{depth} \) — Depth of laying derating from Table 28.1 (direct) or 28.2 (conduit), buried only
• \( F_{resi} \) — Soil resistivity derating from Table 29, buried only
• \( I_{CCC} \) — Base current carrying capacity from the matched StandardColumn

Data Flow

The following diagram shows how installation parameters flow through the system from user input to derated current capacity.

Installation Method + Cable Params ──► CCC Column Lookup (StandardColumn)
                                              │
                                    derating_table_code (D22, D23, etc.)
                                              │
                               Grouping Derating Fields (sidebar v-if)
                                              │
                               Grouping Derating Factor (from AS3008 tables)
                                              │
Installation Method ──────────► Environmental Derating Factors (Tables 27-29)
                                              │
                                F_derating = F_group × F_temp × F_depth × F_resi
                                              │
                                I_derated = F_derating × I_CCC

Key points:

1. CCC sub-selection fields are evaluated before the API call (they select the column)
2. derating_table_code comes back from the API (stored on StandardColumn)
3. Grouping derating fields appear in the sidebar after the first API response
4. Environmental derating fields are always visible based on installation method

Standards & References

Architecture

Code Paths

DERATING_TABLE_MAP = {
    'D22': 'table_22',
    'D23': 'table_23',
    'D24': 'table_24',
    'D25_1': 'table_25_1',
    'D25_2': 'table_25_2',
    'D26_1': 'table_26_1',
    'D26_2': 'table_26_2',
}